The CAN bus system has come into widespread use for the communication between sensors and control units. For example, it is used in automobiles. In the CAN bus system, messages are transmitted using the CAN protocol as described in the CAN specification in ISO11898. Particularly automotive bus systems continuously evolve to higher bandwidths, lower latency times and stricter real-time capability. More recently, additional technologies such as CAN-FD, in which messages are transmitted in accordance with the specification “CAN with Flexible Data Rate, specification version 1.0” (source: http://www.semiconductors.bosch.de), were proposed for this purpose, etc. In such technologies the maximum data rate possible is increased beyond a value of 1 Mbit/s through the use of a higher synchronization in the area of the data fields.
In addition to primarily functional supplementations such as TTCAN, the expansion of the CAN standard with CAN-FD in the recent past was broadened in particular with regard to the possible (higher) data rate and the usable data packet size, while the original CAN characteristics, in particular in the form of the arbitration, were maintained. Furthermore, the signal representation in the data portion was essentially modified by a higher switching frequency of the signal statuses (high/low).
German Patent Application No. DE 10 2009 026961 A1 describes a method for transmitting data between user stations of a bus system. Here, an expansion of the existing CAN signal and the associated communications unit is described with regard to the utilization of high-frequency signals, which is impressed onto the bus line as a CAN data flow in arbitrary form, e.g., temporally in parallel or in embedded form. Proposed in this context in particular is a coordination of the signal, whether a synchronization signal, a trigger signal, with the CAN signal.
In order to further develop the CAN bus system to higher speeds beyond CAN-FD, there are concepts for the corresponding configuration and implementation of the physical layer. In a CAN-based communication, multiple recipients, which are generally connected to the line at different points of the communications bus, receive the transmitted information on a communications bus simultaneously for this purpose.
When a high-rate communication is employed, such as in the center frame portion of a CAN frame, i.e., between frame head and frame end, distortions are created in the received signal in the form of inter-symbol interference (ISI), for example.
For a robust reception, a recipient requires information about the channel status in the form of the current pulse response and about disturbance variables that are present. These variables are generally a function of the current transmitter/recipient pairing, which means, for example, that the pulse response on each receive path (different transmitters) must be known to a recipient in order to ensure that the message is able to be detected in a robust manner through the use of equalization, robust meaning sufficiently fault-free in this context. Given N users TN in the network, there are generally N*(N−1)/2 different pulse responses. This is due to the fact that each connection between two users TN normally has a different pulse response;
this pulse response is independent of a direction at a point in time, i.e., has the same form (reciprocity) for transmitter TN1->recipient TN2 and transmitter TN2->recipient TN1.
Generally, the required variables for the channel characterization, in particular the channel-pulse responses, are not initially known and available on the side of each recipient. Therefore, they must be newly estimated or adapted at regular intervals as a result of temperature effects, among other things. For the estimate, a user transmits, for example, a training sequence known to all sides, and the corresponding channel-pulse response is able to be estimated from its receive signal. This may take place at a plurality of receiving points simultaneously so that the emission of N (orthogonal) sequences is generally sufficient to characterize the entire network.
It is possible to accommodate the training sequence in the frame head of the CAN frame, for instance. However, in this case it is problematic that the emission of the training sequence requires approximately 5-25% of the temporal duration of a CAN frame. Accordingly, this reduces the net data rate of the system as a whole in comparison with the gross data rate inasmuch as the time used for emitting the training sequence is unable to be used for a data transmission. This becomes a particularly glaring problem in systems that have only a few users or user stations.